Fluid displacement system using gerotor pump

ABSTRACT

A fluid displacement system for a fluid producing subterranean well includes a well extending from a surface to a subterranean fluid bearing formation, the formation being in fluid communication with the well; and a gerotor pump in the well for pumping fluid from the formation to the surface.

BACKGROUND OF THE INVENTION

The invention relates to a system and method for pumping fluids from a subterranean well.

Subterranean wells are commonly used for producing fluids such as hydrocarbons and the like from deep underground formations bearing such fluids. In some instances these fluids are sufficiently free-flowing and under sufficient pressure that production through the well to the surface does not need to be assisted. In other instances, the fluids can have an extremely high viscosity, or formation pressure may be too low, or numerous other factors can lead to unsatisfactory flow rates from the well.

Various pumping methods have been used to increase flow from wells including sucker-rod pumps, progressing cavity pumps and electric submersible centrifugal pumps. In fact, each of these systems has issues when needed to operate on highly viscous hydrocarbons such as the heavy and extra heavy crude oils which are contained in the Orinoco Oil Belt.

The ability of centrifugal pumps to handle fluids is impaired by high viscosity. For surface applications where viscous fluids are to be pumped, centrifugal pumps or rotor-dynamical relatives are disregarded in favor of positive displacement pumps. Nevertheless, centrifugal impellers still have an advantage for downhole use. This advantage consists of the easiness to stack many impellers in a cylindrical housing that fits into oil production casing. This design produces a very long pump (30 ft or more) that must be driven by a powerful electric motor. Electric submersible pumps used in the Orinoco Oil Belt are equipped with motors whose power is in the range of 200 HP to 300 HP. A significant amount of power is wasted due to the low mechanical energy conversion capacity of centrifugal pumps. Thus, there is a need for a more efficient pumping device more suitable for handling viscous oils.

Sucker-rod pumps are preferred to produce medium to low flow rates (500 b/d or less). It is possible to achieve larger flow rates but at the expense of using cumbersome, visually unpleasant and expensive surface driving units such as giant walking beams and power cylinders with necessary hydraulic power units. Furthermore, clever as it is, converting rotational motion from prime motor to reciprocating motion to drive the downhole pump implies wasted energy due to incessant acceleration and deceleration of large mechanical parts such as rod strings and surface units.

Thus, the need remains for an improved approach to pumping these fluids. The present invention addresses this need.

SUMMARY OF THE INVENTION

In accordance with the present invention, the forgoing need has been met. According to the invention, a fluid displacement system and method are provided for producing fluids from a subterranean well, and the system and method are based on the use of gerotor pumps which have been found to be particularly effective at pumping highly viscous hydrocarbons.

According to the invention, a fluid displacement system is provided for pumping fluids from a fluid producing subterranean well, which system comprises a well extending from a surface to a subterranean fluid bearing formation, the formation being in fluid communication with the well; and a gerotor pump in the well for pumping fluid from the formation to the surface. Details of the pump are also novel as discussed herein.

In further accordance with the invention, a method is provided for pumping a fluid from a well, which method comprises the steps of positioning a well from a surface to a subterranean formation; placing a gerotor pump in the well; and operating the gerotor pump to drive fluids from the subterranean well to the surface.

Other advantages and details will appear in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of preferred embodiments of the present inventions follows, with reference to the attached drawings, wherein:

FIG. 1 shows a typical well extending from the surface to a subterranean formation and including a gerotor pump according to the present invention;

FIG. 2 illustrates basic components of a gerotor assembly in accordance with the present invention;

FIG. 3 shows rotors of a gerotor pump within an eccentric ring;

FIGS. 4-5 further illustrate the porting disks of a gerotor pump in accordance with the present invention;

FIGS. 6-7 illustrate a gerotor pump with two gerotor sets working in series;

FIGS. 8-9 illustrate a middle casing for use in a multiple pumping stage gerotor pump according to the invention;

FIGS. 10-11 illustrate a middle casing housing two pumping stages to provide a two pumping stage assembly working in parallel;

FIG. 12 illustrates a two stage gerotor assembly with bearing carriers;

FIGS. 13-14 illustrate the inlet bearing carrier of FIG. 12;

FIGS. 15 and 16 illustrate the outlet bearing carrier of FIG. 12; and

FIG. 17 is a cross sectional view of a multistage parallel gerotor pump assembly in accordance with the present invention.

DETAILED DESCRIPTION

The invention relates to a fluid displacement system and method which utilizes gerotor pumps to improve pumping flow rates of heavy and extra heavy crude oils from subterranean wells.

FIG. 1 illustrates a subterranean well 1 extending from the surface 2 to a subterranean formation 3. Formation 3 is typically a permeable formation containing fluids within the void space of the formation, and it is desired to produce these fluids from the formation 3 through well 1 to surface 2.

While useful with a variety of potential different applications, the present invention is particularly well suited for use in producing heavy and extra heavy crude oils such as the heavy crude oil contained in the Orinoco Oil Belt. A typical hydrocarbon from this belt has a viscosity of about 1,000 cP at reservoir temperature (130-140° F.), and this type of fluid is very difficult to pump utilizing conventional sucker-rod pumps, progressing cavity pumps and the like.

In accordance with the invention, a gerotor pump 10 is positioned down hole in well 1 and used to enhance flow of heavy and extra heavy crude oils from the wells in accordance with the present invention. FIG. 1 shows gerotor pump 10 positioned in well 1 at a depth D which may typically be set in the Orinoco Belt at a depth between about 3,000 and about 3,500 feet. The setting depth of this pump is not limited to such values, which can also be greater than 10,000 feet.

A gerotor is a positive displacement pumping unit. The name gerotor is derived from “generated rotor”. A gerotor typically consists of an inner and an outer rotor 16, 18 (FIG. 2). The inner rotor 16 typically has N teeth and the outer rotor 18 typically has N+1 teeth. Centerlines of outer rotor 16 and inner rotor 18 are parallel and separated by a certain eccentricity in order to be properly assembled. With such mating satisfied, both rotors rotate. The geometry of the two rotors partition the space between them into N different dynamically-changing volumes. During the assembly's rotation cycle, each of these volumes changes continuously, so any given volume first increases and then decreases. An increase creates a vacuum, and this creates a suction which draws fluid into the space between the rotors. This is where the intake to the pump can be located. As a volume decreases, fluids can be pumped or compressed, and an outlet can be located at this position. The cylindrical geometry of the gerotor pump makes such pumps suitable for building downhole pumps. Also, their movement is rotational, which is advantageous for using rotating prime movers such as electrical motors and hydraulic motors. Moreover, rotational motion can be also delivered from surface using a rotating rod string as a power transmission shaft.

FIG. 2 illustrates a gerotor set 12 which is a component of gerotor pump 10, and shows a shaft 14 upon which is mounted an inner rotor 16, and about which is engaged an outer rotor 18. As discussed above, rotation of shaft 14 causes pockets to be expanded and then contracted between the inter-meshed gears or teeth of inner rotor 16 and outer rotor 18, and with a proper porting, these pockets can be used to pump fluid. This structure is particularly well structured for pumping highly viscous fluids.

FIG. 3 shows rotors 16, 18 of FIG. 2 positioned within an eccentric ring 20. Eccentric ring 20 is a ring which has a gradually increasing and then gradually decreasing wall thickness. Thus, ring 20 defines an inner cylindrical surface which is not concentric with its outer cylindrical surface. Outer rotor 18 is positioned within eccentric ring 20 as shown. When shaft 14 is rotated, inner rotor 16 and outer rotor 18 also rotate within eccentric ring 20, and the pockets between inter-meshed gears of the rotors 16, 18 expand and contract as desired.

Ring 20 also serves as a journal bearing for outer rotor 18. Outer rotor 18 fits into eccentric ring 20 with the necessary space to allow sliding movement while preventing excessive fluid slippage or leakage.

FIG. 4 shows set 12 with porting disks 22, 24 mounted on either side. FIG. 4 shows porting disk 22 with an inlet 26, and inlet 26 is arranged to be aligned with the space between inter-meshed teeth of the rotors where the space expands. In this fashion, the vacuum created between the teeth of the rotors draws fluids through inlet 26 into the vacuum. As the rotors rotate, the fluid becomes trapped at the precise moment when the space defined by the teeth reaches a maximum volume. With further rotation, the space between rotors decreases, and fluid in the space is compressed. The fluids will be expelled from an outlet 28 (FIG. 5) of porting disk 24 at a significantly higher pressure. Outlet 28 is positioned on disk 24 to coincide with the proper location with respect to the gerotor set 12 where fluids should be expelled.

In accordance with the invention, to enhance pumping volume and speed, gerotor sets 12 can be assembled in series such that fluid discharged from one gerotor set can then be acted upon by another gerotor set. FIG. 6 shows a rotor assembly 21 having a first rotor set 12 and a second rotor set 12′ arranged for operation in series. The first and second rotor sets 12, 12′ are separated by a cylinder or porting disk 24′ which is positioned such that the discharge from first gerotor set 12 coincides with the vacuum and inlet of the second gerotor set 12′. Porting disk 22 is positioned at an inlet end of the assembly. This is also further illustrated in the exploded view of FIG. 7.

Still considering the embodiment of FIG. 6, while the illustrated assembly could itself be an entire pump and have an outlet side porting disk 22′ (FIG. 7), the assembly can also be one stage of a multiple stage unit, and in that circumstance can have an interstage porting disk or middle casing at an outlet end. Such a middle casing is further discussed below.

It should be appreciated with consideration of the illustration of FIGS. 6 and 7 that the eccentric ring 20, 20′ in this embodiment are rotated 180 degrees relative to each other when assembled as shown in FIGS. 6 and 7. In this way, the external gears 18, 18′ acquire the necessary radial placement to generate discharge from the first gerotor set 12 and this discharge is properly aligned with the inlet of the second gerotor set 12′ as shaft 14 rotates. This can be seen in FIG. 7 from considering the position of spaces between teeth of the rotors 16, 18 for each rotor set 12, 12′.

The assembly illustrated in FIGS. 6 and 7 can advantageously be used in multiples to provide a multi-stage system. To this end, for a two stage system, a middle casing 32 is provided and is further illustrated in FIGS. 8 and 9.

Middle casing 32 has openings 33 to house multiple gerotor sets, and ports to feed fluid to and discharge pumped fluid from each gerotor set or stage. FIG. 8 shows casing 32 as a cylindrical member having an opening 33 facing each end, each opening being sized to receive a gerotor assembly. Casing 32 has an inlet 34 positioned inwardly from one opening to receive a discharge of fluid from a first gerotor set or pumping stage. FIG. 9 further illustrates middle casing 32, and shows an internal passage 36 a which conducts fluids from inlet 34 to outlet 36. The passage 36 a defined between inlet 34 and outlet 36 conducts fluids radially outside of a second pumping stage in the other opening, bypassing it. Also shown in FIG. 9 is a second stage inlet 38 which can be defined in the cylindrical wall surrounding the opening for the first stage. Fluids enter through inlet 38 and then are conducted radially inwardly through passage 38 b and discharged through outlet 38 a. Outlet 38 a feeds the second pumping stage. The second stage of such a system can therefore be considered to be operating in parallel to the first stage since its pumping action is independent from the first pumping stage, but both fluid rates are summed up.

FIG. 10 further illustrates the two stage embodiment in accordance with the present invention, and shows middle casing 32 housing two gerotor steps or stages 35, 37 as discussed above. FIG. 11 further illustrates components of this aspect of the invention. FIG. 11 is a cross sectional view and shows middle casing 32 with components of the first gerotor pumping stage 35 which receives fluids at the inlet 26 to the stage, and pumps these fluids to inlet 34 of middle casing 32, through passage 36 a, and to outlet 36. In the meantime, additional fluids are drawn into inlet 38 and through passage 38 a to the radially inwardly located inlet 26′ of second pumping stage 37, and fluids exiting the second pumping stage can then re-join fluids exiting middle casing 32 from the first stage.

FIG. 12 illustrates a further aspect of the invention related to bearing carriers 42, 42′ which can advantageously be positioned on either side of middle casing 32 to support shaft 14. Bearings housed therein can be bushings or antifriction bearings, depending upon the work load to be handled by the pump. The bearings 44, 44′ are mounted in bearing carriers 42, 44′ as shown in FIG. 12. Inlet bearings carrier 42 therefore has openings 46, 46′ which can advantageously be aligned with the inlets to the pumping stages, for example as further illustrated in FIGS. 13 and 14.

As shown in FIGS. 13 and 14, bearing carrier 42 can have two inlets 46, 46′ which can be radially extended openings formed in one face of the carrier. One inlet 46 can lead to a passage 48 which aligns with the inlet to the first pumping stage, while inlet 46′ leads to a passage 48′ which aligns with inlet 38 of middle casing 32. Thus, flow into inlet 46 would be acted upon by the first stage of the pumping unit, while flow through inlet 46′ would be acted upon by the second stage. FIGS. 13 and 14 also further illustrate the bearing bore 50 through which shaft 14 passes, and also illustrates a radially enlarged portion 52 which can house a bearing cover 54 (shown in FIG. 12).

From a consideration of FIGS. 15 and 16 it should be appreciated that the second bearing carrier 42′ can be structurally similar or identical to the first bearing carrier 42, with flow passages properly aligned as shown in FIG. 12 to carry the discharge from both pumping stages, and to pass this flow to outlets having a shape similar to the inlets illustrated in FIG. 14. FIG. 15 shows bearing carrier 42′ from the side which connects to middle casing 32, and shows inlets 56, 56′. Considering also FIG. 16, inlet 56 leads through a passage 58 to an outlet 60, while inlet 56′ leads through a passage 62 to outlet 60′. It should be apparent from FIGS. 12 and 15 that inlet 56 aligned with the outlet of the second stage, while inlet 56′ aligns with outlet 38 a of middle casing 32. Outlet 60, 60′ are radially extending grooves similar in shape to the inlets of inlet bearing carrier 42. In addition, outlet bearing carrier 42′ also has a bearing bore 50′ and can be provided with a radially enlarged portion 52′ for holding bearing 44′, with a bearing cover 54′ securing the bearing in place.

Turning now to FIG. 17, a cross sectional view of an entire assembly of a multi stage pump in accordance with the present invention is illustrated. FIG. 17 shows middle casing 32 housing first and second pumping stages 35, 37, and having bearing carriers 42, 42′ connected at each end of middle casing 32. Shaft 14 passes through both bearing carriers 42, 42′, middle casing 32 and the first and second pumping stages 35, 37, housed therein. Shaft 14 is rotated by an electric motor (not shown), and this rotation causes the rotors of pumping stages 35, 37 to rotate and pump fluid. FIG. 17 shows the two parallel flow paths for fluid being drawn through the multistage pumping system, and again makes clear that these paths are parallel paths, with one being acted upon by first stage 35 and the other being acted upon by second stage 37.

Inlet and outlet connector sections 64, 64′ are also shown in FIG. 17 and would be used to connect the multistage pump unit in accordance with the present invention into or at the end of a production tube for use in increasing flow of fluids from the well and through the tube.

As discussed above, gerotor pump 10 in accordance with the present invention operates through rotation being imparted to shaft 14. Various available structures and methods could be used to impart rotation to shaft 14. One particularly preferred approach in accordance with the present invention is to use an electric submersible motor 80 (FIG. 1), advantageously incorporated into the structure of pump 10 to cause such rotation as desired. Contrary to suggestions made in prior art documents, an electric submersible motor 80 can be positioned in pump 10 and used in the described manner, even at extreme depths, such as depths greater than 10,000 feet deep in a well drilled to a subterranean formation, and such motors are useful for extended periods of time.

Thus, in accordance with the present invention, the driver for the pump is advantageously an electric submersible motor, and it is desirable to position at least one of pump 10 and motor 80, and preferably both of these components, within well 1 at a depth D between 3,000 and 3,500 feet, and even greater than 10,000 feet as needed.

It should be appreciated that the present disclosure has been given in terms of a preferred embodiment. The scope of the invention is not to be viewed as being limited by this embodiment, but rather as being defined by the scope of the appended claims. 

1. A fluid displacement system for a fluid producing subterranean well, comprising: a well extending from a surface to a subterranean fluid bearing formation, the formation being in fluid communication with the well; and a gerotor pump in the well for pumping fluid from the formation to the surface.
 2. The apparatus of claim 1, wherein the gerotor pump is driven by an electric submersible motor.
 3. The apparatus of claim 2, wherein at least one of the gerotor pump and the electric submersible motor is located in the well at a depth from the surface of at least 3,000 feet.
 4. The apparatus of claim 1, wherein the gerotor pump comprises at least one set of inner and outer rotors rotatably engaged within a journal bearing.
 5. The apparatus of claim 1, wherein the journal bearing defines an eccentric inner surface rotatably housing the outer rotor, and wherein the inner rotor engages the outer rotor such that the inner rotor is concentric with an outer cylindrical surface of the journal bearing.
 6. The apparatus of claim 4, wherein the rotors are mounted in the journal bearing between disks having inlet and outlet ports for fluid to be compressed and discharged by the rotors, respectively.
 7. The apparatus of claim 1, wherein the gerotor pump comprises a plurality of gerotor pumps each having at least one set of inner and outer rotors.
 8. The apparatus of claim 7, wherein the plurality of gerotor pumps are communicated with each other in series.
 9. The apparatus of claim 8, wherein the gerotor pumps are communicated in series through an intermediate cylinder having a port aligned with an outlet of a first gerotor pump and an inlet of a second gerotor pump.
 10. The apparatus of claim 6, wherein the plurality of gerotor pumps are communicated in parallel.
 11. The apparatus of claim 10, wherein the plurality of gerotor pumps are communicated in parallel through a middle casing.
 12. The apparatus of claim 11, wherein the middle casing comprises a cylindrical member having a first opening at one end for receiving a first gerotor pump, a second opening at the other end for receiving a second gerotor pump, a central wall separating the first opening from the second opening, an inlet in the central wall aligned within an outlet of the first gerotor pump, the inlet leading through a passage to a radial outlet by passing the second gerotor pump, and a radial inlet defined in a wall surrounding the first opening which leads through a passage that bypasses the first gerotor pump and has an outlet aligned with an inlet of the second gerotor pump.
 13. The apparatus of claim 12, wherein each of the first and second gerotor pumps comprises a pumping stage each having a plurality of gerotor assemblies communicated in series.
 14. The apparatus of claim 12, further comprising an inlet bearing carrier and an outlet bearing carrier, wherein the inlet bearing carrier is mounted to the middle casing at the one end and has a first inlet aligned with the inlet of the first gerotor pump and a second inlet aligned with the radial inlet of the middle casing, and wherein the outlet bearing carrier is mounted to the middle casing at the other end and has a first outlet aligned with the radial outlet of the middle casing and a second outlet aligned with the outlet of the second gerotor pump.
 15. The apparatus of claim 14, wherein the gerotor pumps are mounted on a shaft, and wherein the inlet bearing carrier and the outlet bearing carrier support bearings in which the shaft is rotatably mounted.
 16. A method for pumping a fluid from a well, comprising the steps of: positioning a well from a surface to a subterranean formation; placing a gerotor pump in the well; and operating the gerotor pump to drive fluids from the subterranean well to the surface.
 17. The method of claim 12, wherein the gerotor pump is driven by an electric submersible motor.
 18. The method of claim 13, wherein at least one of the gerotor pump and the electric submersible motor is located in the well at a depth from the surface of at least 3,000 feet. 